Report on Shishaldin (United States) — December 1986
Scientific Event Alert Network Bulletin, vol. 11, no. 12 (December 1986)
Managing Editor: Lindsay McClelland.
Shishaldin (United States) Vigorous steam ejection
Please cite this report as:
Global Volcanism Program, 1986. Report on Shishaldin (United States) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 11:12. Smithsonian Institution.
54.756°N, 163.97°W; summit elev. 2857 m
All times are local (unless otherwise noted)
Vigorous steam ejection was observed on 20 December, and weak to moderate steaming was occasionally visible from late October through late December 1986. The 20 December steam ejection was considerably stronger than Shishaldin's typical activity, but significantly weaker in both size and ash content than the 6-7 May steam and ash emission. [The following reports describing activity at Shishaldin during 27 October-26 December 1986 were collected by John Reeder. Observers were Capts. Jerry Chisum (JC), MarkAir; Capts. Harold Black (HB) and Edward Livingston (EL), Reeve Aleutian Airways; Marcia Brown (MB), FAA, Cold Bay; Capt. Harold Wilson (HW), Peninsula Airways; and Rick Cales (RC), Cold Bay.]
27 October: Steam plume and haze to 80 km SW. (HB, EL)
17 November (1200-1400): Small steam plume to 20 km S; haze to 70 km S. (JC, EL)
18 November: Steam plume and haze to 65 km SW. (JC)
25 November: Unusual volume of steam, drifting ENE. (MB)
2 December: Very little steam (30-m plume). (MB)
15 December (1400): 300-m steam plume. (HW)
20 December (1030): Steam puffs to 600 m above the volcano. (HW)
20 December (1230): Steam blast rose to 2 km above summit in 10 minutes, remaining for 1 hour before slowly subsiding. (HW)
26 December (1800): 300-m vertical steam plume, drifting 8 km NE. (RC)
27-29 December: 300-m vertical steam plume. (MB)
Geologic Background. The beautifully symmetrical Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The glacier-covered volcano is the westernmost of three large stratovolcanoes along an E-W line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." A steam plume often rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the W and NE sides at 1,500-1,800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of Strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century.
Information Contacts: J. Reeder, ADGGS.